Hi Joan. They could very well be migrating or a new juvenile pair looking for a new habitat to call their own. If they have black bills they could be Trumpeter or Tundra swans. Tundra swans have a yellow space (called a lore) between their eye and bill. Mute swans can have a grayish or black bill which will turn reddish orange when they reach approximately one year of age. The Regal Swan